Antioxidant compositions for conventional jet aircraft lubricating fluids, such as fluoroesters and polyphenyl ethers are well known. Such antioxidants are disclosed in Antioxidants For High-Temperature Lubricants, Stemniski et al. ASLE Transactions Vol. 7, p. 43 (1964), and are exemplified by tin-containing compounds such as bis(p-phenoxy phenyl)-diphenyl tin, p-bis(triphenyl stannoxy)-benzene, tetraphenyl tin, tetrakis (p-phenoxy phenyl) tin, bis(p-phenoxy phenyl) tin and diphenyl tin oxide.
As disclosed in Antioxidant Action of Metals and Metal-Organic Salts in Fluoroesters and Polyphenyl Ethers, Ravner et al., J. of Chemical and Engineering Data Vol. 8, No. 4, p. 591 (1963), the oxides, hydroxides and carbonates of the alkaline metals and of barium, and copper salts, steel and stainless steel toluates and benzoates of barium, nickel, lead, praseodymium, manganese, cobalt, chromium, titanium and ytterbium all displayed significant antioxidant activity in fluoroesters and polyphenyl ethers. However, more interest has been recently centering on the use of cyclophosphazene fluids for jet aircraft, turbine, and diesel engine lubricating fluids.
The cyclophosphazene fluids which are of current interest for use in jet aircraft, turbine, and diesel engines are highly advanced fluids or lubricants, as they are required to operate well at extremely high temperatures. Conventional antioxidants for the polyphenyl ether fluids, such as aryl tin compounds, are detrimental to cyclophosphazene fluids. To the inventors' knowledge, the cyclophosphazene fluids are new, and they know of no antioxidants which have yet been developed for use in conjunction with these fluids or lubricants. Unfortunately, attempts by the inventors to produce an oxidation-resistant cyclophosphazene from conventional antioxidants had met with failure due to the volatility and insolubility of the conventional antioxidants when combined with the new cyclophosphazene fluids and lubricants.
Therefore, it is a primary object of the invention to provide a high temperature stable cyclophosphazene with an effective antioxidant to oxidatively stabilize the cyclophosphazene fluids at the extremely high operating temperatures required for use in jet aircraft, turbine, and diesel engines.
It is another object of the present invention to provide a method for solubilizing a non-volatile antioxidant into cyclophosphazene fluids.
It is yet another object of the present invention to provide a formulation and method for preparing cyclophosphazene fluids containing an effective antioxidant in order to improve the upper operating temperature limit of the fluids.
It is yet another object of the invention to provide antioxidants designed to be blended with cyclophosphazene fluids and lubricants.